Flexible polyurethane foams are generally prepared by reacting an organic polyisocyanate and a polyol in the presence of a blowing agent, a catalyst, and a foam stabilizer. Typical polyols used in the art include polyether polyols prepared by alkoxylating an hydroxy-functional initiator. While foams prepared from these polyols are satisfactory for many applications, such foams are often not firm enough for low density foam applications. Firmer foams can be produced by using polymer polyols prepared by polymerizing one or more ethylenically unsaturated monomers in a polyether polyol; dispersions of polyureas and/or polyhydrazodicarbonamides in hydroxyl group containing materials (see, e.g. U.S. Pat. Nos. 4,042,537 and 4,089,835); higher functionality initiators, short chain crosslinkers and/or fillers. However, these solutions lead to other deficiencies such as processing difficulties, closed cells, or poor tear and elongation properties in low density foams.
Isocyanate coupled polyols are known and have been described in the art. The uses of such coupled polyols are varied and include raw materials for use in producing polyurethane elastomers (see, e.g. U.S. Pat. Nos. 3,115,481 and 3,963,681); warp-sizing agents, floculating agents, films and fibers (see, e.g. U.S. Pat. No. 3,054,778); isocyanate terminated prepolymers for use in making foams (see, e.g. U.S. Pat. No. 3,078,239); and, as a portion of the polyol used to produce polymer polyols (see, e.g. U.S. Pat. No. 4,357,430).
Polyols which have been modified with epoxy resins (see, e.g. U.S. Pat. Nos. 4,309,532, 4,316,991 and 4,373,034) and with diepoxides are also known (see, e.g. U.S. Pat. No. 4,045,474).
Despite all these efforts, the use of an isocyanate-coupled polyol to increase the load-bearing properties of a flexible foam has not been suggested.